This invention relates to a detector for detecting the user's hand as it approaches the door handle of an automobile and generating a trigger signal for initiating the automatic unlocking operation of a passive entry system for the automobile. The invention also relates to lock controllers using such a detector.
In recent years, there have been proposals for vehicle entry system apparatus for automatically operating an equipment on a vehicle by carrying out two-way communications between a device carried by the user and a vehicle-mounted main device and thereby carrying out a required comparison, and some of such apparatus are actually coming to be used. With such an apparatus adapted to carry out two-way communications, an answer signal containing a necessary code can be automatically transmitted from the device carried by the user to the main device in response to a request signal (such as a startup signal for starting up the device being carried) transmitted from the main device and hence an equipment on a vehicle can be caused to carry out a specified operation without the user carrying out any operation at all. With a vehicle entry system, for example, the user carrying a portable device may have only to approach the door of a specified vehicle to which a corresponding main device is mounted for establishing a two-way communication between them such that a lock-opening command is automatically outputted to the locked door and the locked door becomes automatically unlocked. Such highly convenient entry systems capable of locking and unlocking a vehicle door basically without requiring any conscious effort on the part of the user are sometimes referred to as a passive entry system (or a smart entry system) as an improved version of general keyless entry systems, and needs for such systems are becoming higher as they are capable of increasing the market values of the vehicles.
If it is attempted with such a passive entry system to save the power of the vehicle battery by transmitting request signals from the main device only when they are necessary, a detector may be required for detecting the user approaching or contacting the vehicle (such as to its door handle).
Optical sensors, capacitance sensors and mechanical switches (so-called micro-switches) have recently been used for such a purpose. Optical sensors are adapted, for example, to detect the user's hand approaching the door handle on the basis of a change in the output from a light-receiving element as light outputted from a light-emitting element is screened or reflected by the user's hand. Capacitance sensors are so-called touch sensors and adapted, as disclosed in Japanese Patent Publication Tokkai 2002-295064, to detect the user's hand approaching the door handle based on a change in the capacitance of a capacitor within the sensor by the contact of the user's hand. Examples of a sensor of a non-contact type include Doppler radars used for a startup switch device for an automatic door, as disclosed in Japanese Patent 2785893.
Prior art technologies characterized as using a detector as explained above have problems as explained below.
(A) Optical sensors may function incorrectly in the presence of unwanted objects such as rain drops and dead leaves or due to the incidence of light from a lamp or sunlight, while capacitance sensors are weak against noise as a matter of principle and tend to function incorrectly in the presence of dielectric matters such as rain drops.
(B) Response characteristics of optical, capacitance and mechanical sensors are not sufficient because their detection areas are small (or their detection distance is short) and the system depending on such a sensor may function incorrectly. If such a sensor is set to the door handle of a vehicle for providing a trigger for the transmission of a request signal in a passive entry system of the vehicle, for example, the user's hand may not be detected and hence the request signal may not be outputted until the hand nearly touches the sensor. Thus, the user may be already starting to pull the handle in order to open the door but the door may not be unlocked yet. In other words, the user may try to open the locked door quickly by using a passive entry system but its automatic unlocking operation may be delayed and the door may refuse to open immediately. In the case of a capacitance sensor or a mechanical switch, in particular, detection is not made until the user's hand makes a firm contact with the sensor. If the detector is of a kind having such a sensor simply attached to the door, the communication to the portable unit is completed and the door is unlocked only after the user begins to pull the handle in order to open it. Thus, this problem does not fail to appear.
(C) Since sensor elements which are relatively large and hence are difficult to be contained must be provided to a vehicle component such as a door handle intended to detect the approaching target object of detection, the shape and the size of such a component may have to be modified significantly to accommodate such sensor elements and hence the freedom in its design is severely restricted. In particular, when it is desired to detect the user's hand approaching the door handle of a vehicle with a response characteristic as high as possible by using an optical sensor or a mechanical switch, a light-emitting element and a light-receiving element must be placed near the door handle or a contact probe of a mechanical switch must be placed at a position protruding from the door handle. Thus, the design of the door handle or the body parts of the vehicle in the vicinity is severely affected, In the case of a capacitance sensor, a relatively bulky electrode must be buried inside the handle and this also limits the freedom in the design.
As explained above, Doppler radars used for automatic doors are known examples of sensors of a non-contact type capable of providing a large detection area and not affected by dirt or the like. Thus, it may be considered to use such a Doppler radar as the detector for a passive entry system, but prior art Doppler radars are for detecting the speed and direction of the motion of a target object of detection on the basis of changes in the frequency of received waves and cannot be used directly for detecting a target object approaching within a short distance by means of a simple structure. The device according to aforementioned Japanese Patent 2785893, for example, is adapted to carry out complicated judging processes with its signal processor comprising a microcomputer, its power consumption rate is high and the signal processor becomes big, requiring a large space for its setting. Thus, it is not feasible to be used as the detector for a vehicle which uses battery cells as its power source and is strongly required to be energy-saving and compact.
It is therefore an object of this invention to make use of the technology of Doppler radars to provide an improved detector superior in operational reliability, response characteristics, and capability of being mounted to a vehicle (from the points of view of size, freedom in design and power consumption).
It is another object of this invention to provide a lock controller using such a detector.